Resist compositions and patterning process

ABSTRACT

A resist composition contains a base resin, a photoacid generator, and a solvent. The photoacid generator is a sulfonium salt of formula (1).  
                 
 
     R 1  is a monovalent cyclic or bridgedring C 3-20 , hydrocarbon group, R 2  is hydroxyl, nitro, halogen, or a straight, branched or cyclic monovalent C 1-15  hydrocarbon group which may contain O, N, S or halogen atom, K −  is a non nucleophilic counter ion, x is equal to 1 or 2, and y is an integer of 0-3. The resist composition is sensitive to ArF excimer laser light, has good sensitivity and resolution, and forms a thick film which is advantageous in etching.

[0001] This invention relates to a resist composition comprising aspecific sulfonium salt as the photoacid generator, for use withradiation having a wavelength of up to 200 nm, especially ArF excimerlaser light, F₂ excimer laser light, EUV, x-ray and electron beam (EB),and a patterning process using the same.

BACKGROUND OF THE INVENTION

[0002] While a number of recent efforts are being made to achieve afiner pattern rule in the drive for higher integration and operatingspeeds in LSI devices, deep-ultraviolet lithography is thought to holdparticular promise as the next generation in microfabricationtechnology. In particular, photolithography using an ArF excimer laseras the light source is strongly desired to reach the practical level asthe micropatterning technique capable of achieving a feature size of 0.2μm or less.

[0003] In the photolithography using an ArF excimer laser (wavelength193 nm) as the light source, a high sensitivity resist material capableof achieving a high resolution at a small dose of exposure is needed toprevent the degradation of precise and expensive optical systemmaterials. Among several measures for providing a high sensitivityresist material, the most common is to select each component which ishighly transparent at the wavelength of 193 nm. For example, polyacrylicacid and derivatives thereof, norbornenemaleic anhydride alternatingcopolymers, polynorbornene and metathesis ringopening polymers have beenproposed as the base resin. This choice is effective in that thetransparency of a resin alone is increased. However, the photoacidgenerator has the problem that increasing its transparency leads to adrop of acid generation efficiency, resulting in a low sensitivity orthe lack of thermal stability and storage stability. There is availableno photoacid generator which is practically acceptable.

[0004] For example, JP-A 7-25846, JP-A 7-28237 and JP-A 8-27102 disclosealkylsulfonium salts which are highly transparent, but unsatisfactory inacid generation efficiency and thermal stability. JP-A 10-319581discloses alkylarylsulfonium salts which have a high sensitivity and agood balance of transparency and acid generation efficiency, but lackthermal stability and storage stability. Arylsulfonium salts, which areregarded effective in photolithography using a KrF excimer laser, aregood in acid generation efficiency, thermal stability and storagestability, but very low transparent to ArF excimer laser light so thatthe pattern resulting from exposure and development is noticeablytapered. The lack of transparency can be compensated for by thinning theresist, but such a thin resist film is less resistant to etching. Thisis inadequate as the pattern forming process.

SUMMARY OF THE INVENTION

[0005] An object of the invention is to provide a highly resolvableresist composition comprising a photoacid generator having a highsensitivity to ArF excimer laser light as well as thermal stability andstorage stability. Another object is to provide a patterning processusing the resist composition.

[0006] It has been found that a sulfonium salt of the following generalformula (1) has a high sensitivity to ArF excimer laser light as well assatisfactory thermal stability and storage stability and that a resistcomposition having the sulfonium salt blended therein has a highresolution and is fully suited for precise micropatterning.

[0007] The invention provides a resist composition comprising a baseresin, a photoacid generator, and a solvent. The photoacid generator isa sulfonium salt of the following general formula (1).

[0008] Herein R¹ is a monovalent cyclic or bridgedring hydrocarbon groupof 3 to 20 carbon atoms, R² is hydroxyl, nitro, halogen, or a straight,branched or cyclic monovalent hydrocarbon group of 1 to 15 carbon atomswhich may contain an oxygen, nitrogen, sulfur or halogen atom, K⁻ is anon-nucleophilic counter ion, x is equal to 1 or 2, and y is an integerof 0 to 3.

[0009] In one preferred embodiment, the base resin is a polymer havingan alicyclic structure. The base resin is typically at least one polymerselected from the group consisting of polyacrylic acid and derivativethereof, a ternary or quaternary copolymer of a norbornenederivative-maleic anhydride alternating polymer and polyacrylic acid orderivative thereof, a ternary or quaternary copolymer of atetracyclododecene derivativemaleic anhydride alternating polymer andpolyacrylic acid or derivative thereof, a ternary or quaternarycopolymer of a norbornene derivative-maleimide alternating polymer andpolyacrylic acid or derivative thereof, a ternary or quaternarycopolymer of a tetracyclododecene derivativemaleimide alternatingpolymer and polyacrylic acid or derivative thereof, polynorbornene, andmetathesis ringopened polymer.

[0010] In a further preferred embodiment, the base resin is a polymercomprising recurring units of the following general formula (2) andhaving a weight average molecular weight of 1,000 to 500,000.

[0011] Herein R⁰⁰¹ is hydrogen, methyl or CH₂CO₂R⁰⁰³; R⁰⁰² is hydrogen,methyl or CO₂R⁰⁰³; R⁰⁰³ is a straight, branched or cyclic alkyl group of1 to 15 carbon atoms; R⁰⁰⁴ is hydrogen or a monovalent hydrocarbon groupof 1 to 15 carbon atoms having a carboxyl or hydroxyl group; at leastone of R⁰⁰⁵ to R⁰⁰⁸ represents a monovalent hydrocarbon group of 1 to 15carbon atoms having a carboxyl or hydroxyl group while the remaining R'sindependently represent hydrogen or a straight, branched or cyclic alkylgroup of 1 to 15 carbon atoms, R⁰⁰⁵ to R⁰⁰⁸, taken together, may form aring, and in that event, at least one of R⁰⁰⁵ to R⁰⁰⁸ is a divalenthydrocarbon group of 1 to 15 carbon atoms having a carboxyl or hydroxylgroup while the remaining R's are independently single bonds orstraight, branched or cyclic alkylene groups of 1 to 15 carbon atoms;R⁰⁰⁹ is a monovalent hydrocarbon group of 3 to 15 carbon atomscontaining a —CO₂— partial structure; at least one of R⁰¹⁰ to R⁰¹³ is amonovalent hydrocarbon group of 2 to 15 carbon atoms containing a —CO₂—partial structure, while the remaining R's are independently hydrogen orstraight, branched or cyclic alkyl groups of 1 to 15 carbon atoms, R⁰¹⁰to R⁰¹³, taken together, may form a ring, and in that event, at leastone of R⁰¹⁰ to R⁰¹³ is a divalent hydrocarbon group of 1 to 15 carbonatoms containing a —CO₂— partial structure, while the remaining R's areindependently single bonds or straight, branched or cyclic alkylenegroups of 1 to 15 carbon atoms; R⁰¹⁴ is a polycyclic hydrocarbon grouphaving 7 to 15 carbon atoms or an alkyl group containing a polycyclichydrocarbon group; R⁰¹⁵ is an acid labile group; R⁰¹⁶ is a methylenegroup or oxygen atom; R⁰¹⁷ is a single bond or a straight, branched orcyclic alkylene group of 1 to 10 carbon atoms which may have a heteroatomcontaining substituent; R⁰¹⁸ is hydrogen or an alkyl group of 1 to10 carbon atoms; k is equal to 0 or 1; a1, a2, a3, b1, b2, b3, c1, c2,c3, d1, d2, d3, and e are numbers from 0 to less than 1, satisfyinga1+a2+a3+b1+b2+b3+c1+c2+c3+d1+d2+d3+e=1.

[0012] In another aspect, the invention provides a chemically amplified,positive resist composition comprising a photoacid generator of thegeneral formula (1); a base resin as defined above which issubstantially insoluble in a developer, but becomes soluble in thedeveloper under the action of an acid; and a solvent. Preferably, theresist composition further includes a basic compound.

[0013] In a further aspect, the invention provides a chemicallyamplified, negative resist composition comprising a photoacid generatorof the general formula (1); a crosslinker; a base resin as defined abovewhich is soluble in a developer, but becomes insoluble in the developerafter being crosslinked with the crosslinker under the action of anacid; and a solvent. Preferably, the negative resist composition furtherincludes a basic compound.

[0014] In a still further aspect, the invention provides a process forforming a resist pattern comprising the steps of applying a resistcomposition as defined above onto a substrate to form a coating; heattreating the coating and then exposing it to radiation having awavelength of up to 200 nm through a photo mask; and optionally heattreating the exposed coating and developing it with a developer.

[0015] The sulfonium salt of the formula (1) has a very high sensitivityto ArF excimer laser light so that even when blended in a small amount,it can generate a sufficient amount of acid. Then a resist compositionhaving the sulfonium salt blended therein has a high sensitivity andhigh transparency, forms a pattern having high rectangularity followingexposure and development, and is advantageous in etching because of noneed for film thinning. The inventive sulfonium salt eliminates the lackof thermal stability and storage stability which is the drawback ofprior art alkylsulfonium salts and alkylarylsulfonium salts.

[0016] In the sulfonium salt of the formula (1), one or two aryl groupsare introduced at the sacrifice of transparency to some extent. However,the introduction of aryl group(s) improves acid generation efficiencyoutstandingly and as a consequence, enables to enhance sensitivity. Whenthe sensitivity to light of 193 nm wavelength is compared between resistfilms having the same transmittance, the sulfonium salt of formula (1)improves the sensitivity by a factor of at least 3 over thearylsulfonium salts. The problem of thermal stability and storagestability that the prior art salts suffer from has been overcome byselecting cyclic alkyl groups.

[0017] It is noted that the sulfonium salt of formula (1) is highlysensitive to radiation with a wavelength of less than 200 nm, especiallyArF excimer laser light, and not useful in photolithography using KrFexcimer laser light of 248 nm wavelength.

DESCRIPTION OF THE PREFERRED EMBODIMENT

[0018] Sulfonium salt

[0019] The resist composition of the invention contains a sulfonium saltof the general formula (1).

[0020] Herein R¹ is a monovalent cyclic hydrocarbon group of 3 to 20carbon atoms which may be a bridgedring hydrocarbon group; R² is ahydroxyl group, nitro group, halogen atom, or straight, branched orcyclic monovalent hydrocarbon group of 1 to 15 carbon atoms which maycontain an oxygen, nitrogen, sulfur or halogen atom; K⁻ is anonnucleophilic counter ion; x is equal to 1 or 2, and y is an integerof 0 to 3.

[0021] More particularly, R¹ stands for monovalent cyclic hydrocarbongroups of 3 to 20 carbon atoms, for example, cyclopropyl, cyclobutyl,cyclopentyl, cyclohexyl, norbornyl, and adamantyl. R² stands forhydroxyl groups, nitro groups, halogen atoms, or straight, branched orcyclic monovalent hydrocarbon groups of 1 to 15 carbon atoms which maycontain O, N, S or a halogen atom, for example, alkyl groups such asmethyl, ethyl, tert-butyl, and cyclohexyl. Some hydrogen atoms on thesegroups may be replaced by groups containing an O, N or S atom, such ashydroxyl, oxo, nitro or mercapto groups. K⁻ is a nonnucleophilic counterion, for example, halide ions such as chloride ion and bromide ion,triflate, fluoroalkylsulfonates such as 1,1,1-trifluoroethanesulfonateand nonafluorobutanesulfonate, arylsulfonates such as tosylate,benzenesulfonate, 4-fluorobenzenesulfonate, and1,2,3,4,5-pentafluorobenzenesulfonate, and alkylsulfonates such asmesylate and butanesulfonate. Letter x is an integer of 1 or 2, and y isan integer of 0 to 3, preferably equal to 0, 1 or 2, and more preferablyequal to 0 or 1.

[0022] Illustrative, nonlimiting, examples of the sulfonium salt offormula (1) which is formulated in the resist composition according tothe invention are given below.

[0023] In the resist composition according to the invention, thesulfonium salt of formula (1) is preferably formulated in an amount ofabout 0.1 to 15 parts, especially about 0.5 to 8 parts by weight per 100parts by weight of the base resin (all parts are by weight,hereinafter). Less amounts of the sulfonium salt may lead to lowsensitivity. Excessive amounts of the sulfonium salt may detract fromtransparency, resulting in a resist composition with an inferiorresolving power.

[0024] In one preferred embodiment, the resist composition uses as thebase resin a polymer or high molecular weight compound comprisingrecurring units of the following general formula (2) and having a weightaverage molecular weight of about 1,000 to 500,000, especially about5,000 to 100,000.

[0025] Herein, R⁰⁰¹ is hydrogen, methyl or CH₂CO₂R⁰⁰³.

[0026] R⁰⁰² is hydrogen, methyl or CO₂R⁰⁰³.

[0027] R⁰⁰³ is a straight, branched or cyclic alkyl group of 1 to 15carbon atoms, for example, methyl, ethyl, propyl, isopropyl, n-butyl,sec-butyl, tert-butyl, tert-amyl, n-pentyl, n-hexyl, cyclopentyl,cyclohexyl, ethylcyclopentyl, butylcyclopentyl, ethylcyclohexyl,butylcyclohexyl, adamantyl, ethyladamantyl, and butyladamantyl.

[0028] R⁰⁰⁴ is hydrogen or a monovalent hydrocarbon group (preferablystraight, branched or cyclic alkyl group) of 1 to 15 carbon atoms havinga carboxyl or hydroxyl group, for example, carboxyethyl, carboxybutyl,carboxycyclopentyl, carboxycyclohexyl, carboxynorbornyl,carboxyadamantyl, hydroxyethyl, hydroxybutyl, hydroxycyclopentyl,hydroxycyclohexyl, hydroxynorbornyl, and hydroxyadamantyl.

[0029] At least one of R⁰⁰⁵ to R⁰⁰⁸ represents a monovalent hydrocarbongroup (preferably straight, branched or cyclic alkyl group) of 1 to 15carbon atoms having a carboxyl or hydroxyl group while the remaining R'sindependently represent hydrogen or a straight, branched or cyclic alkylgroup of 1 to 15 carbon atoms. Examples of the carboxyl orhydroxylbearing monovalent hydrocarbon group of 1 to 15 carbon atomsinclude carboxy, carboxymethyl, carboxyethyl, carboxybutyl,hydroxymethyl, hydroxyethyl, hydroxybutyl, 2-carboxyethoxycarbonyl,4-carboxybutoxycarbonyl, 2-hydroxy ethoxycarbonyl,4-hydroxybutoxycarbonyl, carboxycyclopentyl oxycarbonyl,carboxycyclohexyloxycarbonyl, carboxynorbornyl oxycarbonyl,carboxyadamantyloxycarbonyl, hydroxycyclopentyloxycarbonyl,hydroxycyclohexyloxycarbonyl, hydroxynorbornyloxycarbonyl, andhydroxyadamantyloxycarbonyl. Examples of the straight, branched orcyclic alkyl group of 1 to 15 carbon atoms are the same as exemplifiedfor R⁰⁰³.

[0030] Alternatively, R⁰⁰⁵ to R⁰⁰⁸, taken together, may form a ring, andin that event, at least one of R⁰⁰⁵ to R⁰⁰⁸ is a divalent hydrocarbongroup (preferably straight or branched alkylene group) of 1 to 15 carbonatoms having a carboxyl or hydroxyl group, while the remaining R's areindependently single bonds or straight, branched or cyclic alkylenegroups of 1 to 15 carbon atoms. Examples of the carboxyl orhydroxyl-bearing divalent hydrocarbon group of 1 to 15 carbon atomsinclude the groups exemplified as the carboxyl or hydroxyl-bearingmonovalent hydrocarbon group, with one hydrogen atom eliminatedtherefrom. Examples of the straight, branched or cyclic alkylene groupsof 1 to 15 carbon atoms include the groups exemplified for R⁰⁰³, withone hydrogen atom eliminated therefrom.

[0031] R⁰⁰⁹ is a monovalent hydrocarbon group of 3 to 15 carbon atomscontaining a —CO₂— partial structure, for example, 2-oxooxolan-3-yl,4,4-dimethyl-2-oxooxolan-3-yl, 4-methyl-2-oxooxan-4-yl,2-oxo-1,3-dioxolan-4-ylmethyl, and 5-methyl-2oxooxolan-5-yl.

[0032] At least one of R⁰¹⁰ to R⁰¹³ is a monovalent hydrocarbon group of2 to 15 carbon atoms containing a —CO₂— partial structure, while theremaining R's are independently hydrogen or straight, branched or cyclicalkyl groups of 1 to 15 carbon atoms. Examples of the monovalenthydrocarbon group of 2 to 15 carbon atoms containing a —CO₂— partialstructure include 2-oxooxolan-3-yloxycarbonyl,4,4-dimethyl-2-oxooxolan-3-yloxycarbonyl,4-methyl-2-oxooxan-4-yloxycarbonyl,2-oxo-1,3-dioxolan-4-ylmethyloxycarbonyl, and5-methyl-2-oxooxolan-5-yloxycarbonyl. Examples of the straight, branchedor cyclic alkyl groups of 1 to 15 carbon atoms are the same asexemplified for R⁰⁰³.

[0033] R⁰¹⁰ to R⁰¹³, taken together, may form a ring, and in that event,at least one of R⁰¹⁰ to R⁰¹³ is a divalent hydrocarbon group of 1 to 15carbon atoms containing a —CO₂— partial structure, while the remainingR's are independently single bonds or straight, branched or cyclicalkylene groups of 1 to 15 carbon atoms. Examples of the divalenthydrocarbon group of 1 to 15 carbon atoms containing a—CO₂— partialstructure include 1-oxo-2-oxapropane-1,3-diyl,1,3-dioxo-2-oxapropane-1,3-diyl, 1-oxo-2-oxabutane-1,4-diyl, and1,3-dioxo-2-oxabutane-1,4-diyl, as well as the groups exemplified as themonovalent hydrocarbon group containing a —CO₂— partial structure, withone hydrogen atom eliminated therefrom. Examples of the straight,branched or cyclic alkylene groups of 1 to 15 carbon atoms include thegroups exemplified for R⁰⁰³, with one hydrogen atom eliminatedtherefrom.

[0034] R⁰¹⁴ is a polycyclic hydrocarbon group having 7 to 15 carbonatoms or an alkyl group containing a polycyclic hydrocarbon group, forexample, norbornyl, bicyclo[3.3.1]-nonyl, tricyclo[5.2.1.0]decyl,adamantyl, ethyladamantyl, butyladamantyl, norbornylmethyl, andadamantylmethyl.

[0035] R⁰¹⁵ is an acid labile group.

[0036] R⁰¹⁶ is a methylene group or oxygen atom.

[0037] R⁰¹⁷ is a single bond or a straight, branched or cyclic alkylenegroup of 1 to 10 carbon atoms which may have a hetero atom-containingsubstituent such as hydroxy, alkoxy or acetyl.

[0038] R⁰¹⁸ is hydrogen or an alkyl group of 1 to 10 carbon atoms.

[0039] Letter k is equal to 0 or 1; a1, a2, a3, b1, b2, b3, c1, c2, c3,d1, d2, d3, and e are numbers from 0 to less than 1, satisfyinga1+a2+a3+b1+b2+b3+c1+c2+c3+d1+d2+d3+e=1.

[0040] Illustrative examples of the acid labile group represented byR⁰¹⁵ include groups of the following formulae (L1) to (L5), tertiaryalkyl groups of 4 to 20 carbon atoms, preferably 4 to 15 carbon atoms,trialkylsilyl groups whose alkyls each have 1 to 6 carbon atoms, andoxoalkyl groups of 4 to 20 carbon atoms.

[0041] Herein, R^(L01) and R^(L02) each are hydrogen or a straight,branched or cyclic alkyl group of 1 to 18 carbon atoms, preferably 1 to10 carbon atoms, for example, methyl, ethyl, propyl, isopropyl, n-butyl,sec-butyl, sect-butyl, cyclopentyl, cyclohexyl, 2-ethylhexyl, andn-octyl. R^(L03) is a monovalent hydrocarbon group of 1 to 18 carbonatoms, preferably 1 to 10 carbon atoms, which may have a hetero atomsuch as an oxygen atom, for example, straight, branched or cyclic alkylgroups, in which some hydrogen atoms may be replaced by hydroxyl,alkoxy, oxo, amino, or alkylamino groups. More illustrative of theR^(L03) group are the substituted alkyl groups shown below.

[0042] —(CH₂)₄—OH —(CH₂)₂—O—(CH₂ ₃—CH₃

[0043] —(CH₂)₂—O—(CH₂)₂—OH —(CH₂)₆—OH

[0044] A pair of R^(L01) ad R^(L02), a pair of R^(L01) and R^(L03), or apair of R^(L02) and R^(L03), taken together, may form a ring. R^(L01),R^(L02) and R^(L03) each represent straight or branched alkylene groupsof 1 to 18 carbon atoms, preferably 1 to 10 carbon atoms when they forma ring.

[0045] R^(L04) is a tertiary alkyl group of 4 to 20 carbon atoms,preferably 4 to 15 carbon atoms, trialkylsilyl group whose alkyls eachhave 1 to 6 carbon atoms, oxoalkyl group of 4 to 20 carbon atoms, orgroup of above formula (L1). Exemplary tertiary alkyl groups includesect-butyl, tert-amyl, 1,1-diethylpropyl, 1-ethylcyclopentyl,1-butylcyclopentyl, 1-ethylcyclohexyl, 1-butylcyclohexyl,1-ethyl-2-cyclopentenyl, 1-ethyl-2-cyclohexenyl, and2-methyl-2-adamantyl. Exemplary trialkylsilyl groups are trimethylsilyl,triethylsilyl and dimethyl-sect-butylsilyl. Examples of oxoalkyl groupsinclude 3-oxocyclohexyl, 4-methyl-2-oxooxan-4-yl, and5-methyl-5-oxooxolan-4-yl. The letter “a” is an integer of 0 to 6.

[0046] R^(L05) is a straight, branched or cyclic alkyl group of 1 to 8carbon atoms or substituted or unsubstituted aryl group of 6 to 20carbon atoms. Exemplary straight, branched or cyclic alkyl groupsinclude methyl, ethyl, propyl, isopropyl, n-butyl, sec-butyl,sect-butyl, tert-amyl, n-pentyl, n-hexyl, cyclopentyl, cyclohexyl,cyclopentylmethyl, cyclopentylethyl, cyclohexylmethyl, andcyclohexylethyl. Exemplary substituted or unsubstituted aryl groupsinclude phenyl, methylphenyl, naphthyl, anthryl, phenanthryl, andpyrenyl. The letter m is equal to 0 or 1, and n is equal to 0, 1, 2, or3, satisfying 2m+n=2 or 3.

[0047] R^(L06) is a straight, branched or cyclic C₁₋₈ alkyl group or asubstituted or unsubstituted C₆₋₂₀ aryl group. Examples of these groupsare as exemplified for R^(L05) .

[0048] R^(L07) to R^(L06) are independently hydrogen or C₁₋₁₅ monovalenthydrocarbon groups which may contain a hetero atom. Examples of thehydrocarbon groups include straight, branched or cyclic alkyl groupssuch as methyl, ethyl, propyl, isopropyl, n-butyl, sec-butyl,sect-butyl, tert-amyl, n-pentyl, n-hexyl, n-octyl, n-nonyl, n-decyl,cyclopentyl, cyclohexyl, cyclopentylmethyl, cyclopentylethyl,cyclopentylbutyl, cyclohexylmethyl, cyclohexylethyl and cyclohexylbutyl;and substituted groups in which some of the hydrogen atoms on theforegoing groups are replaced by hydroxyl, alkoxy, carboxyl,alkoxycarbonyl, oxo, amino, alkylamino, cyano, mercapto, alkylthio andsulfo groups. Any pair of R^(L07) to R^(L16) (e.g., a pair of R^(L07)and R^(L08), a pair of R^(L07) and R^(L09), a pair of R^(L08) andR^(L10), a pair of R^(L09) and R^(L10), a pair of R^(L11) and R^(L12),and a pair of R^(L13) and R^(L14)) may form a ring. When these R's inpair form a ring, they are independently divalent C₁₋₁₅ hydrocarbongroups which may contain a hetero atom, examples of which are the sameas exemplified above for the monovalent hydrocarbon groups, with onehydrogen atom eliminated therefrom. Also any pair of R^(L07) to R^(L16)(e.g., a pair of R^(L07) and R^(L09), a pair of R^(L09) and R^(L15), anda pair of R^(L13) and R^(L15)) may form a single bond so that a doublebond is formed between the carbon and the carbon to which these R's areattached.

[0049] Of the acid labile groups of formula (L1), straight and branchedgroups are illustrated below.

[0050] —CH₂—O—CH₃ —CH₂—O—CH₂—CH₃ —CH₂—O—(CH₂)₂—CH₃

[0051] CH₂—O—(CH₂)₃—CH₃

[0052] Of the acid labile groups of formula (L1), exemplary cyclicgroups include tetrahydrofuran-2-yl, 2-methyltetrahydrofuran-2-yl,tetrahydropyran-2-yl and 2-methyltetrahydropyran-2-yl.

[0053] Illustrative examples of the acid labile group of formula (L2)include sect-butoxycarbonyl, sect-butoxy carbonylmethyl,tert-amyloxycarbonyl, tert-amyloxycarbonyl-methyl,1,1-diethylpropyloxycarbonyl, 1,1-diethylpropyloxy carbonylmethyl,1-ethylcyclopentyloxycarbonyl, 1-ethyl-cyclopentyloxycarbonylmethyl,1-ethyl-2-cyclopentenyloxycarbonyl,1-ethyl-2-cyclopentenyloxycarbonylmethyl, 1-ethoxyethoxycarbonyl-methyl,2-tetrahydropyranyloxycarbonylmethyl, and2-tetrahydrofuranyloxycarbonylmethyl.

[0054] Illustrative examples of the acid labile group of formula (L3)include 1-methylcyclopentyl, 1-ethylcyclopentyl, 1-n-propylcyclopentyl,1-isopropylcyclopentyl, 1-n-butylcyclopentyl, 1-sec-butylcyclopentyl,1-methylcyclohexyl, 1-ethylcyclohexyl, 3-methyl-1-cyclopenten-3-yl,3-ethyl-1-cyclopenten-3-yl, 3-methyl-1-cyclohexen-3-yl, and3-ethyl-1-cyclohexen-3-yl.

[0055] Illustrative examples of the acid labile group of formula (L4)are given below.

[0056] Examples of the tertiary alkyl, trialkylsilyl and oxoalkyl groupsincluded in the acid labile group represented by R⁰¹⁵ are the same asexemplified above.

[0057] Illustrative examples of the acid labile group of formula (L5)are given below.

[0058] The polymer formulated in the inventive resist composition has aweight average molecular weight of about 1,000 to 500,000, preferablyabout 3,000 to 100,000. Outside the range, the etching resistance maybecome extremely low and the resolution may become low because asubstantial difference in rate of dissolution before and after exposureis lost.

[0059] The polymer is not limited to one type and a mixture of two ormore polymers may be added. The use of plural polymers allows for easyadjustment of resist properties.

[0060] In the resist composition of the invention, a compound other thanthe sulfonium salt of formula (1) may be formulated as the photoacidgenerator.

[0061] Photoacid generator

[0062] The additional photoacid generator which can be used hereinincludes the following:

[0063] (i) onium salts of the formula (P1a1), (P1a2) or (P1b),

[0064] (ii) diazomethane derivatives of the formula (P2),

[0065] (iii) glyoxime derivatives of the formula (P3),

[0066] (iv) bissulfone derivatives of the formula (P4),

[0067] (v) sulfonic acid esters of Nhydroxyimide compounds of theformula (P5),

[0068] (vi) Pketosulfonic acid derivatives,

[0069] (vii) disulfone derivatives,

[0070] (viii) nitrobenzylsulfonate derivatives, and

[0071] (ix) sulfonate derivatives.

[0072] These photoacid generators are described in detail.

[0073] (i) Onium salts of formula (P1a1), (P1a2) or (P1b):

[0074] Herein, R^(101a), R^(101b), and R^(101c) independently representstraight, branched or cyclic alkyl, alkenyl, oxoalkyl or oxoalkenylgroups of 1 to 12 carbon atoms, aryl groups of 6 to 20 carbon atoms, oraralkyl or aryloxoalkyl groups of 7 to 12 carbon atoms, wherein some orall of the hydrogen atoms may be replaced by alkoxy or other groups.Also, R^(101b) and R^(101c), taken together, may form a ring. R^(101b)and R^(101c) each are alkylene groups of 1 to 6 carbon atoms when theyform a ring. K⁻ is a nonnucleophilic counter ion.

[0075] R^(101a), R^(101b), and R^(101c) may be the same or different andare illustrated below. Exemplary alkyl groups include methyl, ethyl,propyl, isopropyl, n-butyl, sec-butyl, tert-butyl, pentyl, hexyl,heptyl, octyl, cyclopentyl, cyclohexyl, cycloheptyl, cyclopropylmethyl,4-methylcyclohexyl, cyclohexylmethyl, norbornyl, and adamantyl.Exemplary alkenyl groups include vinyl, allyl, propenyl, butenyl,hexenyl, and cyclohexenyl. Exemplary oxoalkyl groups include2-oxocyclopentyl and 2-oxocyclohexyl as well as 2-oxopropyl,2-cyclopentyl-2-oxoethyl, 2-cyclohexyl-2-oxoethyl, and2-(4-methylcyclohexyl)-2-oxoethyl. Exemplary aryl groups include phenyland naphthyl; alkoxyphenyl groups such as p-methoxyphenyl,m-methoxyphenyl, o-methoxyphenyl, ethoxyphenyl, p-sect-butoxyphenyl, andm-sect-butoxyphenyl; alkylphenyl groups such as 2-methylphenyl,3-methylphenyl, 4-methylphenyl, ethylphenyl, 4-sect-butylphenyl,4-butylphenyl, and dimethylphenyl; alkylnaphthyl groups such asmethylnaphthyl and ethylnaphthyl; alkoxynaphthyl groups such asmethoxynaphthyl and ethoxynaphthyl; dialkylnaphthyl groups such asdimethylnaphthyl and diethylnaphthyl; and dialkoxynaphthyl groups suchas dimethoxynaphthyl and diethoxynaphthyl. Exemplary aralkyl groupsinclude benzyl, phenylethyl, and phenethyl. Exemplary aryloxoalkylgroups are 2-aryl-2-oxoethyl groups such as 2-phenyl-2-oxoethyl,2-(1-naphthyl)-2-oxoethyl, and 2-(2-naphthyl)-2-oxoethyl. Examples ofthe nonnucleophilic counter ion represented by K⁻ include halide ionssuch as chloride and bromide ions, fluoroalkylsulfonate ions such astriflate, 1,1,1-trifluoro ethanesulfonate, andnonafluorobutanesulfonate, arylsulfonate ions such as tosylate,benzenesulfonate, 4-fluorobenzenesulfonate, and1,2,3,4,5-pentafluorobenzene sulfonate, and alkylsulfonate ions such asmesylate and butanesulfonate.

[0076] Herein, R^(102a) and R^(102b) independently represent straight,branched or cyclic alkyl groups of 1 to 8 carbon atoms. R¹⁰³ representsa straight, branched or cyclic alkylene groups of 1 to 10 carbon atoms.R^(104a) and R^(104b) independently represent 2-oxoalkyl groups of 3 to7 carbon atoms. K⁻ is a non-nucleophilic counter ion.

[0077] Illustrative of the groups represented by R^(102a) and R^(102b)are methyl, ethyl, propyl, isopropyl, n-butyl, sec-butyl, sect-butyl,pentyl, hexyl, heptyl, octyl, cyclopentyl, cyclohexyl,cyclopropylmethyl, 4-methylcyclohexyl, and cyclohexylmethyl.Illustrative of the groups represented by R¹⁰³ are methylene, ethylene,propylene, butylene, pentylene, hexylene, heptylene, octylene, nonylene,1,4-cyclohexylene, 1,2-cyclohexylene, 1,3-cyclopentylene,1,4-cyclooctylene, and 1,4-cyclohexanedimethylene. Illustrative of thegroups represented by R^(104a) and R^(104b) are 2-oxopropyl,2-oxocyclopentyl, 2-oxocyclohexyl, and 2-oxocycloheptyl. Illustrativeexamples of the counter ion represented by K are the same as exemplifiedfor formulae (P1a1) and (P1a2).

[0078] (ii) Diazomethane derivatives of formula (P2)

[0079] Herein, R¹⁰⁵ and R¹⁰⁶ independently represent straight, branchedor cyclic alkyl or halogenated alkyl groups of 1 to 12 carbon atoms,aryl or halogenated aryl groups of 6 to 20 carbon atoms, or aralkylgroups of 7 to 12 carbon atoms.

[0080] Of the groups represented by R¹⁰⁵ and R¹⁰⁶, exemplary alkylgroups include methyl, ethyl, propyl, isopropyl, n-butyl, sec-butyl,sect-butyl, pentyl, hexyl, heptyl, octyl, amyl, cyclopentyl, cyclohexyl,cycloheptyl, norbornyl, and adamantyl. Exemplary halogenated alkylgroups include trifluoromethyl, 1,1,1-trifluoroethyl,1,1,1-trichloroethyl, and nonafluorobutyl. Exemplary aryl groups includephenyl; alkoxyphenyl groups such as p-methoxyphenyl, m-methoxyphenyl,o-methoxyphenyl, ethoxyphenyl, p-sect-butoxyphenyl, andm-sect-butoxyphenyl; and alkylphenyl groups such as 2-methylphenyl,3-methylphenyl, 4-methylphenyl, ethylphenyl, 4-tert-butylphenyl,4-butylphenyl, and dimethylphenyl. Exemplary halogenated aryl groupsinclude fluorophenyl, chlorophenyl, and 1,2,3,4,5-pentafluorophenyl.Exemplary aralkyl groups include benzyl and phenethyl.

[0081] (iii) Glyoxime derivatives of formula (P3)

[0082] Herein, R¹⁰⁷, R¹⁰⁶, and R¹⁰⁹ independently represent straight,branched or cyclic alkyl or halogenated alkyl groups of 1 to 12 carbonatoms, aryl or halogenated aryl groups of 6 to 20 carbon atoms, oraralkyl groups of 7 to 12 carbon atoms. Also, R¹⁰⁸ and R¹⁰⁹, takentogether, may form a ring. R¹⁰⁸ and R¹⁰⁹ each are straight or branchedalkylene groups of 1 to 6 carbon atoms when they form a ring.

[0083] Illustrative examples of the alkyl, halogenated alkyl, aryl,halogenated aryl, and aralkyl groups represented by R¹⁰⁷, R¹⁰⁸, and R¹⁰⁹are the same as exemplified for R¹⁰⁵ and R¹⁰⁶ Examples of the alkylenegroups represented by R¹⁰⁸ and R¹⁰⁹ include methylene, ethylene,propylene, butylene, and hexylene.

[0084] (iv) Bissulfone derivatives of formula (P4)

[0085] Herein, R^(101a) and R^(101b) are as defined above.

[0086] (v) Sulfonic acid esters of Nhydroxyimide compounds of formula(P5)

[0087] Herein, R¹¹⁰ is an arylene group of 6 to 10 carbon atoms,alkylene group of 1 to 6 carbon atoms, or alkenylene group of 2 to 6carbon atoms wherein some or all of the hydrogen atoms may be replacedby straight or branched alkyl or alkoxy groups of 1 to 4 carbon atoms,nitro, acetyl, or phenyl groups. R¹¹¹ is a straight, branched or cyclicalkyl group of 1 to 8 carbon atoms, alkenyl, alkoxyalkyl, phenyl ornaphthyl group wherein some or all of the hydrogen atoms may be replacedby alkyl or alkoxy groups of 1 to 4 carbon atoms, phenyl groups (whichmay have substituted thereon an alkyl or alkoxy of 1 to 4 carbon atoms,nitro, or acetyl group), heteroaromatic groups of 3 to 5 carbon atoms,or chlorine or fluorine atoms.

[0088] Of the groups represented by R¹¹⁰, exemplary arylene groupsinclude 1,2-phenylene and 1,8-naphthylene; exemplary alkylene groupsinclude methylene, 1,2-ethylene, 1,3-propylene, 1,4-butylene,1-phenyl-1,2-ethylene, and norbornane-2,3-diyl; and exemplary alkenylenegroups include 1,2-vinylene, 1-phenyl-1,2-vinylene, and5-norbornene-2,3-diyl. Of the groups represented by R¹¹¹, exemplaryalkyl groups are as exemplified for R^(101a) to R^(101c); exemplaryalkenyl groups include vinyl, 1-propenyl, allyl, 1-butenyl, 3-butenyl,isoprenyl, 1-pentenyl, 3-pentenyl, 4-pentenyl, dimethylallyl, 1-hexenyl,3-hexenyl, 5-hexenyl, 1-heptenyl, 3-heptenyl, 6-heptenyl, and 7-octenyl;and exemplary alkoxyalkyl groups include methoxymethyl, ethoxymethyl,propoxymethyl, butoxymethyl, pentyloxymethyl, hexyloxymethyl,heptyloxymethyl, methoxyethyl, ethoxyethyl, propoxyethyl, butoxyethyl,pentyloxyethyl, hexyloxyethyl, methoxypropyl, ethoxypropyl,propoxypropyl, butoxypropyl, methoxybutyl, ethoxybutyl, propoxybutyl,methoxypentyl, ethoxypentyl, methoxyhexyl, and methoxyheptyl.

[0089] Of the substituents on these groups, the alkyl groups of 1 to 4carbon atoms include methyl, ethyl, propyl, isopropyl, n-butyl, isobutyland sect-butyl; the alkoxy groups of 1 to 4 carbon atoms includemethoxy, ethoxy, propoxy, isopropoxy, n-butoxy, isobutoxy, andtert-butoxy; the phenyl groups which may have substituted thereon analkyl or alkoxy of 1 to 4 carbon atoms, nitro, or acetyl group includephenyl, tolyl, p-sect-butoxyphenyl, p-acetylphenyl and p-nitrophenyl;the heteroaromatic groups of 3 to 5 carbon atoms include pyridyl andfuryl.

[0090] Illustrative examples of the photoacid generator include:

[0091] onium salts such as diphenyliodonium trifluoro methanesulfonate,(p-sect-butoxyphenyl)phenyliodonium trifluoromethanesulfonate,diphenyliodonium p-toluene-sulfonate,(p-sect-butoxyphenyl)phenyliodonium p-toluene-sulfonate,triphenylsulfonium trifluoromethanesulfonate,(p-sect-butoxyphenyl)diphenylsulfonium trifluoromethanesulfonate,bis(p-sect-butoxyphenyl)phenylsulfonium trifluoromethanesulfonate,tris(p-sect-butoxyphenyl)sulfonium trifluoromethanesulfonate,triphenylsulfonium p-toluenesulfonate,(p-sect-butoxyphenyl)diphenylsulfonium p-toluenesulfonate,bis(p-sect-butoxyphenyl)phenylsulfonium p-toluenesulfonate,tris(p-sect-butoxyphenyl)sulfonium p-toluenesulfonate,triphenylsulfonium nonafluorobutanesulfonate, triphenylsulfoniumbutanesulfonate, trimethylsulfonium trifluoromethanesulfonate,trimethylsulfonium p-toluenesulfonate,cyclohexylmethyl(2-oxocyclohexyl)sulfonium trifluoromethanesulfonate,cyclohexylmethyl(2-oxocyclohexyl)sulfonium p-oluenesulfonate,dimethylphenylsulfonium trifluoromethanesulfonate,dimethylphenylsulfonium ptoluenesulfonate, dicyclohexylphenylsulfoniumtrifluoromethanesulfonate, dicyclohexylphenylsulfoniump-toluenesulfonate, trinaphthylsulfonium trifluoromethanesulfonate,cyclohexylmethyl-(2-oxocyclohexyl)sulfonium trifluoromethanesulfonate,(2-norbornyl)methyl(2-oxocyclo hexyl)sulfoniumtrifluoromethanesulfonate, ethylenebis[methyl(2-oxocyclopentyl)sulfonium trifluoromethane sulfonate], and1,2′-naphthylcarbonylmethyltetrahydro 5 -thiophenium triflate;

[0092] diazomethane derivatives such asbis(benzenesulfonyl)diazomethane, bis(ptoluenesulfonyl)diazomethane,bis(xylenesulfonyl)diazomethane, bis(cyclohexylsulfonyl)diazomethane,bis(cyclopentylsulfonyl)diazomethane, bis(n-butylsulfonyl)diazomethane,bis(isobutylsulfonyl)diazomethane, bis(sec-butylsulfonyl)diazomethane,bis(n-propylsulfonyl)diazomethane, bis(isopropylsulfonyl)diazomethane,bis(sect-butylsulfonyl)diazomethane, bis(n-amylsulfonyl)diazomethane,bis(isoamylsulfonyl)diazomethane, bis(sec-amylsulfonyl)diazomethane,bis(tert-amylsulfonyl)diazomethane,1-cyclohexylsulfonyll(tert-butylsulfonyl)diazomethane,1-cyclohexylsulfonyl-1(tert-amylsulfonyl)diazomethane, and1-tert-amylsulfonyl-1-(tert-butylsulfonyl)diazomethane;

[0093] glyoxime derivatives such asbiso(p-toluene-sulfonyl)-α-dimethylglyoxime,bis-o-(p-toluenesulfonyl)-α-diphenylglyoxime,bis-o-(p-toluenesulfonyl)-α-dicyclohexylglyoxime,bis-o-(p-toluenesulfonyl)-2,3-pentanedioneglyoxime,bis-o-(p-toluenesulfonyl)-2-methyl-3,4-pentanedioneglyoxime,bis-o-(n-butanesulfonyl)-α-dimethylglyoxime,bis-o-(n-butanesulfonyl)-α-diphenylglyoxime,bis-o-(n-butanesulfonyl)-α-dicyclohexylglyoxime,bis-o-(n-butane-sulfonyl)-2,3-pentanedioneglyoxime,bis-o-(n-butane-sulfonyl)-2-methyl-3,4-pentanedioneglyoxime,bis-o-(methanesulfonyl)-α-dimethylglyoxime,bis-o-(trifluoro-methanesulfonyl)-α-dimethylglyoxime,bis-o-(1,1,1-trifluoroethanesulfonyl)-α-dimethylglyoxime,bis-o-(tertbutanesulfonyl)-α-dimethylglyoxime,bis-o-(perfluorooctanesulfonyl)-α-dimethylglyoxime,bis-o-(cyclohexane-sulfonyl)-α-dimethylglyoxime,bis-o-(benzenesulfonyl)-α-dimethylglyoxime,bis-o-(p-fluorobenzenesulfonyl)-α-dimethylglyoxime,bis-o-(p-sect-butylbenzenesulfonyl)-α-dimethylglyoxime,bis-o-(xylenesulfonyl)-α-dimethylglyoxime, andbis-o-(camphorsulfonyl)-α-dimethylglyoxime;

[0094] bissulfone derivatives such as bisnaphthylsulfonylmethane,bistrifluoromethylsulfonylmethane, bismethylsulfonylmethane,bisethylsulfonylmethane, bispropylsulfonyl methane,bisisopropylsulfonylmethane, bis-p-toluenesulfonylmethane, andbisbenzenesulfonylmethane;

[0095] β-ketosulfone derivatives such as2-cyclohexylcarbonyl-2-(p-toluenesulfonyl)propane and2-isopropylcarbonyl-2-(p-toluenesulfonyl)propane;

[0096] disulfone derivatives such as diphenyl disulfone and dicyclohexyldisulfone;

[0097] nitrobenzyl sulfonate derivatives such as 2,6-dinitrobenzylp-toluenesulfonate and 2,4-dinitrobenzyl p-toluenesulfonate;

[0098] sulfonic acid ester derivatives such as1,2,3-tris(methanesulfonyloxy)benzene,1,2,3-tris(trifluoromethanesulfonyloxy)benzene, and1,2,3-tris(p-toluenesulfonyloxy)benzene; and

[0099] sulfonic acid esters of N-hydroxyimides such as N-hydroxysuccinimide methanesulfonate, N-hydroxysuccinimidetrifluoromethanesulfonate, N-hydroxysuccinimide ethanesulfonate,N-hydroxysuccinimide 1-propanesulfonate,N-hydroxysuccinimide-2-propanesulfonate, N-hydroxysuccinimide1-pentanesulfonate, N-hydroxysuccinimide 1-octanesulfonate,N-hydroxysuccinimide p-toluenesulfonate, N-hydroxysuccinimidep-methoxybenzenesulfonate, N-hydroxysuccinimide 2-chloroethanesulfonate,N-hydroxysuccinimide benzenesulfonate, N-hydroxysuccinimide2,4,6-trimethylbenzenesulfonate, N-hydroxysuccinimide1-naphthalenesulfonate, N-hydroxysuccinimide 2-naphthalenesulfonate,N-hydroxy-2-phenylsuccinimide methanesulfonate, N-hydroxymaleimidemethanesulfonate, N-hydroxymaleimide ethanesulfonate,N-hydroxy-2-phenylmaleimide methanesulfonate, N-hydroxyglutarimidemethanesulfonate, N-hydroxyglutarimide benzenesulfonate,N-hydroxyphthalimide methanesulfonate, N-hydroxyphthalimidebenzenesulfonate, N-hydroxyphthalimide trifluoromethanesulfonate,N-hydroxyphthalimide p-toluenesulfonate, N-hydroxynaphthalimidemethanesulfonate, N-hydroxynaphthalimide benzenesulfonate,N-hydroxy5-norbornene-2,3-dicarboxyimide methanesulfonate,N-hydroxy-5-norbornene-2,3-dicarboxyimide trifluoromethanesulfonate, andN-hydroxy-5-norbornene-2,3-dicarboxyimide ptoluenesulfonate.

[0100] Preferred among these photoacid generators are onium salts suchas triphenylsulfonium trifluoromethanesulfonate,(psect-butoxyphenyl)diphenylsulfonium trifluoromethanesulfonate,tris(p-sect-butoxyphenyl)sulfonium trifluoromethanesulfonate,triphenylsulfonium p-toluenesulfonate,(p-sect-butoxyphenyl)diphenylsulfonium p-toluenesulfonate,tris(p-sect-butoxyphenyl)sulfonium p-toluenesulfonate,trinaphthylsulfonium trifluoromethanesulfonate,cyclohexylmethyl(2-oxocyclohexyl)sulfonium trifluoromethanesulfonate,(2-norbornyl)methyl(2-oxocylohexyl)sulfonium trifluoromethanesulfonate,and 1,2′-naphthyl carbonylmethyltetrahydrothiophenium triflate;diazomethane derivatives such as bis(benzenesulfonyl)diazomethane,bis(p-toluenesulfonyl)diazomethane, bis(cyclohexylsulfonyl)diazomethane,bis(n-butylsulfonyl)diazomethane, bis(isobutylsulfonyl)diazomethane,bis(sec-butylsulfonyl)diazomethane, bis(n-propylsulfonyl)diazomethane,bis(isopropylsulfonyl)diazomethane, andbis(tert-butylsulfonyl)diazomethane; glyoxime derivatives such asbiso(p-toluenesulfonyl)adimethylglyoxime andbis-o-(n-butanesulfonyl)adimethylglyoxime; bissulfone derivatives suchas bisnaphthylsulfonylmethane; and sulfonic acid esters ofN-hydroxyimide compounds such as N-hydroxysuccinimide methanesulfonate,N-hydroxysuccinimide trifluoromethanesulfonate, N-hydroxysuccinimide1-propanesulfonate, N-hydroxysuccinimide 2-propanesulfonate,N-hydroxysuccinimide 1-pentanesulfonate, N-hydroxy succinimidep-toluenesulfonate, N-hydroxynaphthalimide methanesulfonate, andN-hydroxynaphthalimide benzenesulfonate.

[0101] These photoacid generators may be used singly or in combinationsof two or more thereof. Onium salts are effective for improvingrectangularity, while diazomethane derivatives and glyoxime derivativesare effective for reducing standing waves. The combination of an oniumsalt with a diazomethane or a glyoxime derivative allows for fineadjustment of the profile.

[0102] The amount of the photoacid generator and the sulfonium salt offormula (1) combined is preferably about 0.1 to 15 parts, and especiallyabout 0.5 to 8 parts by weight, per 100 parts by weight of the baseresin. Less than 0.1 part of the photoacid generator would provide apoor sensitivity whereas more than 15 parts of the photoacid generatorwould lower the transparency and resolution of resist compositions.

[0103] Organic solvent

[0104] The organic solvent used herein may be any organic solvent inwhich the base resin, photoacid generator, and other components aresoluble. Illustrative, nonlimiting, examples of the organic solventinclude ketones such as cyclohexanone and methyl-2-n-amylketone;alcohols such as 3-methoxybutanol, 3-methyl-3-methoxybutanol,1-methoxy-2-propanol, and 1-ethoxy-2-propanol; ethers such as propyleneglycol monomethyl ether, ethylene glycol monomethyl ether, propyleneglycol monoethyl ether, ethylene glycol monoethyl ether, propyleneglycol dimethyl ether, and diethylene glycol dimethyl ether; and esterssuch as propylene glycol monomethyl ether acetate, propylene glycolmonoethyl ether acetate, ethyl lactate, ethyl pyruvate, butyl acetate,methyl 3-methoxypropionate, ethyl 3-ethoxypropionate, tertbutyl acetate,sect-butyl propionate, and propylene glycol mono-sect-butyl etheracetate. These solvents may be used alone or in combinations of two ormore thereof. Of the above organic solvents, it is recommended to usediethylene glycol dimethyl ether and 1-ethoxy-2-propanol because thephotoacid generator serving as one of the resist components is mostsoluble therein, propylene glycol monomethyl ether acetate because it isa safe solvent, or a mixture thereof.

[0105] An appropriate amount of the organic solvent used is about 200 to1,000 parts, especially about 400 to 800 parts by weight per 100 partsby weight of the base resin.

[0106] Dissolution regulator

[0107] A dissolution regulator may be added to the resist composition.Typical dissolution regulators are compounds having an average molecularweight within a range of 100 to 1,000, and preferably 150 to 800, andbearing on the molecule at least two phenolic hydroxyl groups in which 0to 100 mol %, on the average, of the hydrogen atoms of the phenolichydroxyl groups are substituted with acid labile groups, and compoundshaving a similar average molecular weight and bearing on the molecule atleast one carboxyl group in which 80 to 100 mol %, on the average, ofthe hydrogen atoms of the carboxyl groups are substituted with acidlabile groups.

[0108] It is noted that the percent substitution of hydrogen atoms ofphenolic hydroxyl groups or carboxyl groups with acid labile groups is,on the average, at least 0 mol %, preferably at least 30 mol %, based onthe entire phenolic hydroxyl groups or carboxyl groups, with the upperlimit of percent substitution being 100 mol %, preferably 80 mol %.

[0109] Preferable examples of such compounds having two or more phenolichydroxyl groups or compounds having one or more carboxyl groups includethose of formulas (D1) to (D14) below.

[0110] In these formulas, R²⁰¹ and R²⁰² are each hydrogen or a straightor branched alkyl or alkenyl of 1 to 8 carbon atoms; R²⁰³ is hydrogen, astraight or branched alkyl or alkenyl of 1 to 8 carbon atoms, or-(R²⁰⁷)_(h)—COOH; R²⁰⁴ is -(CH₂)_(i)- (where i=2 to 10), an arylene of 6to 10 carbon atoms, carbonyl, sulfonyl, an oxygen atom, or a sulfuratom; R²⁰⁵ is an alkylene of 1 to 10 carbon atoms, an arylene of 6 to 10carbon atoms, carbonyl, sulfonyl, an oxygen atom, or a 10 sulfur atom;R²⁰⁶ is hydrogen, a straight or branched alkyl or alkenyl of 1 to 8carbon atoms, or a hydroxylsubstituted phenyl or naphthyl; R²⁰⁷ is astraight or branched alkylene of 1 to 10 carbon atoms; R²⁰⁸ is hydrogenor hydroxyl; the letter j is an integer from 0 to 5; u and h are each 0or 1; s, t, s′, t′, s″, and t″ are each numbers which satisfy s+t=8,s′+t′=5, and s″+t″=4, and are such that each phenyl skeleton has atleast one hydroxyl group; and a is a number such that the compounds offormula (D8) or (D9) may have a molecular weight of 100 to 1,000.

[0111] In the above formulas, suitable examples of R²⁰¹ and R²⁰² includehydrogen, methyl, ethyl, butyl, propyl, ethynyl, and cyclohexyl;suitable examples of R²⁰³ include the same groups as for R²⁰¹ and R²⁰²,as well as —COOH and —CH₂COOH; suitable examples of R²⁰⁴ includeethylene, phenylene, carbonyl, sulfonyl, oxygen, and sulfur; suitableexamples of R²⁰⁵ include methylene as well as the same groups as forR²⁰⁴; and suitable examples of R²⁰⁶ include hydrogen, methyl, ethyl,butyl, propyl, ethynyl, cyclohexyl, and hydroxylsubstituted phenyl ornaphthyl.

[0112] Exemplary acid labile groups on the dissolution regulator includegroups of the following general formulae (L1) to (L5), tertiary alkylgroups of 4 to 20 carbon atoms, trialkylsilyl groups in which each ofthe alkyls has 1 to 6 carbon atoms, and oxoalkyl groups of 4 to 20carbon atoms.

[0113] Herein, R^(L01) to R^(L16), a, m and n are as defined andexemplified above.

[0114] The dissolution regulator may be formulated in an amount of 0 toabout 50 parts, preferably about 5 to 50 parts, and more preferablyabout 10 to 30 parts by weight, per 100 parts by weight of the baseresin, and may be used singly or as a mixture of two or more thereof.Less than 5 parts of the dissolution regulator may fail to yield animproved resolution, whereas the use of more than 50 parts would lead tothinning of the patterned film, and thus a decline in resolution.

[0115] The dissolution regulator can be synthesized by introducing acidlabile groups into a compound having phenolic hydroxyl or carboxylgroups in accordance with an organic chemical formulation.

[0116] Basic compound

[0117] In the resist composition of the invention, a basic compound maybe blended. A suitable basic compound used herein is a compound capableof suppressing the rate of diffusion when the acid generated by thephotoacid generator diffuses within the resist film. The inclusion ofthis type of basic compound holds down the rate of acid diffusion withinthe resist film, resulting in better resolution. In addition, itsuppresses changes in sensitivity following exposure, thus reducingsubstrate and environment dependence, as well as improving the exposurelatitude and the pattern profile.

[0118] Examples of basic compounds include primary, secondary, andtertiary aliphatic amines, mixed amines, aromatic amines, heterocyclicamines, carboxyl groupbearing nitrogenous compounds, sulfonylgroupbearing nitrogenous compounds, hydroxyl groupbearing nitrogenouscompounds, hydroxyphenyl groupbearing nitrogenous compounds, alcoholicnitrogenous compounds, amide derivatives, and imide derivatives.

[0119] Examples of suitable primary aliphatic amines include ammonia,methylamine, ethylamine, n-propylamine, isopropylamine, n-butylamine,iso-butylamine, sec-butylamine, tert-butylamine, pentylamine,tert-amylamine, cyclopentylamine, hexylamine, cyclohexylamine,heptylamine, octylamine, nonylamine, decylamine, dodecylamine,cetylamine, methylenediamine, ethylenediamine, andtetraethylenepentamine. Examples of suitable secondary aliphatic aminesinclude dimethylamine, diethylamine, d-in-propylamine,di-iso-propylamine, di-n-butylamine, di-iso-butylamine,di-sec-butylamine, dipentylamine, dicyclopentylamine, dihexylamine,dicyclohexylamine, diheptylamine, dioctylamine, dinonylamine,didecylamine, didodecylamine, dicetylamine, N,N-dimethylmethylenediamine, N,N-dimethylethylenediamine, andN,N-dimethyltetraethylenepentamine. Examples of suitable tertiaryaliphatic amines include trimethylamine, triethylamine,tri-n-propylamine, tri-iso-propylamine, tri-n-butylamine,tri-iso-butylamine, tri-sec-butylamine, tripentylamine,tricyclopentylamine, trihexylamine, tricyclohexylamine, triheptylamine,trioctylamine, trinonylamine, tridecylamine, tridodecylamine,tricetylamine, N,N,N′,N′-tetramethylmethylenediamine,N,N,N′,N′-tetramethylethylenediamine, andN,N,N′,N′-tetramethyltetraethylenepentamine.

[0120] Examples of suitable mixed amines include dimethyl ethylamine,methylethylpropylamine, benzylamine, phenethylamine, andbenzyldimethylamine. Examples of suitable aromatic and heterocyclicamines include aniline derivatives (e.g., aniline, N-methylaniline,N-ethylaniline, N-propylaniline, N,N-dimethylaniline, 2-methylaniline,3-methylaniline, 4-methylaniline, ethylaniline, propylaniline,trimethylaniline, 2-nitroaniline, 3-nitroaniline, 4-nitroaniline,2,4-dinitroaniline, 2,6-dinitroaniline, 3,5-dinitroaniline, andN,N-dimethyltoluidine), diphenyl(p-tolyl)amine, methyldiphenylamine,triphenylamine, phenylenediamine, naphthylamine, diaminonaphthalene,pyrrole derivatives (e.g., pyrrole, 2H-pyrrole, 1-methylpyrrole,2,4-dimethylpyrrole, 2,5-dimethylpyrrole, and N-methylpyrrole), oxazolederivatives (e.g., oxazole and isooxazole), thiazole derivatives (e.g.,thiazole and isothiazole), imidazole derivatives (e.g., imidazole,4-methylimidazole, and 4-methyl-2-phenylimidazole), pyrazolederivatives, furazan derivatives, pyrroline derivatives (e.g., pyrrolineand 2-methyl-1-pyrroline), pyrrolidine derivatives (e.g., pyrrolidine,N-methylpyrrolidine, pyrrolidinone, and N-methylpyrrolidone),imidazoline derivatives, imidazolidine derivatives, pyridine derivatives(e.g., pyridine, methylpyridine, ethylpyridine, propylpyridine,butylpyridine, 4-(1-butylpentyl)pyridine, dimethylpyridine,trimethylpyridine, triethylpyridine, phenylpyridine,3-methyl-2-phenylpyridine, 4tertbutylpyridine, diphenylpyridine,benzylpyridine, methoxypyridine, butoxypyridine, dimethoxypyridine,1-methyl-2-pyridine, 4-pyrrolidinopyridine, 1-methyl-4-phenylpyridine,2-(1-ethylpropyl)pyridine, aminopyridine, and dimethylaminopyridine),pyridazine derivatives, pyrimidine derivatives, pyrazine derivatives,pyrazoline derivatives, pyrazolidine derivatives, piperidinederivatives, piperazine derivatives, morpholine derivatives, indolederivatives, isoindole derivatives, 1-Hindazole derivatives, indolinederivatives, quinoline derivatives (e.g., quinoline and3-quinolinecarbonitrile), isoquinoline derivatives, cinnolinederivatives, quinazoline derivatives, quinoxaline derivatives,phthalazine derivatives, purine derivatives, pteridine derivatives,carbazole derivatives, phenanthridine derivatives, acridine derivatives,phenazine derivatives, 1,10-phenanthroline derivatives, adeninederivatives, adenosine derivatives, guanine derivatives, guanosinederivatives, uracil derivatives, and uridine derivatives.

[0121] Examples of suitable carboxyl groupbearing nitrogenous compoundsinclude aminobenzoic acid, indolecarboxylic acid, and amino acidderivatives (e.g. nicotinic acid, alanine, alginine, aspartic acid,glutamic acid, glycine, histidine, isoleucine, glycylleucine, leucine,methionine, phenylalanine, threonine, lysine,3-aminopyrazine-2-carboxylic acid, and methoxyalanine). Examples ofsuitable sulfonyl groupbearing nitrogenous compounds include3-pyridinesulfonic acid and pyridinium p-toluenesulfonate. Examples ofsuitable hydroxyl group bearing nitrogenous compounds, hydroxyphenylgroupbearing nitrogenous compounds, and alcoholic nitrogenous compoundsinclude 2-hydroxypyridine, aminocresol, 2,4-quinolinediol,3-indolemethanol hydrate, monoethanolamine, diethanolamine,triethanolamine, N-ethyldiethanolamine, N,N-diethylethanolamine,triisopropanolamine, 2,2′-iminodiethanol, 2-aminoethanol,3-amino1-propanol, 4-amino-1-butanol, 4-(2-hydroxyethyl)morpholine,2-(2-hydroxyethyl)pyridine, 1-(2-hydroxyethyl)piperazine,1-[-2-(2-hydroxyethoxy)ethyl]-piperazine, piperidine ethanol,1-(2-hydroxyethyl)pyrrolidine, 1-(2-hydroxyethyl)-2-pyrrolidinone,3-piperidino-1,2-propanediol, 3-pyrrolidino-1,2-propanediol,8-hydroxyjulolidine, 3-quinuclidinol, 3-tropanol, 1-methyl-2-pyrrolidineethanol, 1-aziridine ethanol, N-(2-hydroxyethyl)phthalimide, andN-(2-hydroxyethyl)isonicotinamide. Examples of suitable amidederivatives include formamide, N-methylformamide, N,N-dimethylformamide,acetamide, N-methylacetamide, N,N-dimethylacetamide, propionamide, andbenzamide. Suitable imide derivatives include phthalimide, succinimide,and maleimide.

[0122] In addition, basic compounds of the following general formulas(B1) and (B2) may also be included.

[0123] In the formulas, R³⁰¹, R³⁰², R³⁰³, R³⁰⁷ and R³⁰⁸ independentlystraight, branched or cyclic alkylenes of 1 to 20 carbon atoms; R³⁰⁴,R³⁰⁵, R³⁰⁶, R³⁰⁹ and R³¹⁰ are hydrogen, alkyls of 1 to 20 carbon atoms,or amino; R³⁰⁴ and R³⁰⁵, R³⁰⁴ and R³⁰⁶, R³⁰⁵ and R³⁰⁷, R³⁰⁴ with R³⁰⁵and R³⁰⁶, and R³⁰⁹ and R³¹⁰ may bond together to form rings; and S, Tand U are each integers from 0 to 20, with the proviso that hydrogen isexcluded from R³⁰⁴, R³⁰⁵, R³⁰⁶, R³⁰⁹ and R³¹⁰ when S, T and U are equalto 0.

[0124] The alkylene groups represented by R³⁰¹, R³⁰², R³⁰³, R³⁰⁷ andR³⁰⁸ preferably have 1 to 20 carbon atoms, more preferably 1 to 10carbon atoms, and most preferably 1 to 8 carbon atoms. Examples includemethylene, ethylene, n-propylene, isopropylene, n-butylene, isobutylene,n-pentylene, isopentylene, hexylene, nonylene, decylene, cyclopentylene,and cyclohexylene.

[0125] The alkyl groups represented by R³⁰⁴, R³⁰⁵, R³⁰⁶, R³⁰⁹ and R³¹⁰preferably have 1 to 20 carbon atoms, more preferably 1 to 8 carbonatoms, and most preferably 1 to 6 carbon atoms, and may be straight,branched or cyclic. Examples include methyl, ethyl, n-propyl, isopropyl,n-butyl, isobutyl, tert butyl, n-pentyl, isopentyl, hexyl, nonyl, decyl,dodecyl, tridecyl, cyclopentyl, and cyclohexyl.

[0126] Where R³⁰⁴ and R³⁰⁵, R³⁰⁴ and R³⁰⁶, R³⁰⁵ and R³⁰⁶, R³⁰⁴ with R³⁰⁵and R³⁰⁶, and R³⁰⁹ and R³¹⁰ form rings, the rings preferably have 1 to20 carbon atoms, more preferably 1 to 8 carbon atoms, and mostpreferably 1 to 6 carbon atoms, and may have branching alkyl groups of 1to 6 carbon atoms, and especially 1 to 4 carbon atoms.

[0127] S, T, and U are each integers from 0 to 20, preferably from 1 to10, and more preferably from 1 to 8.

[0128] Illustrative examples of the compounds of formulas (B1) and (B2)include tris{2-(methoxymethoxy)ethyl}amine,tris{2-(methoxyethoxy)ethyl}amine,tris[2-{(2-methoxyethoxy)methoxy}ethyl]amine,tris{2-(2-methoxyethoxy)ethyl}amine,tris(2-(1-methoxyethoxy)ethyl}amine, tris{2-(1-ethoxyethoxy)ethyl}amine,tris{2-(1-ethoxypropoxy)ethyl}amine,tris[2-{(2-hydroxyethoxy)ethoxy}ethyl]amine,4,7,13,16,21,24-hexaoxa-1,10-diazabicyclo[8.8.8]hexacosane,4,7,13,18-tetraoxa-1,10-diazabicyclo[8.5.5]eicosane,1,4,10,13-tetraoxa-7,16-diazabicyclooctadecane,1-aza-12-crown4,1-aza-15-crown-5, and 1-aza-18-crown6. Especiallypreferred basic compounds are tertiary amines, aniline derivatives,pyrrolidine derivatives, pyridine derivatives, quinoline derivatives,amino acid derivatives, hydroxyl groupbearing nitrogenous compounds,hydroxyphenyl group bearing nitrogenous compounds, alcoholic nitrogenouscompounds, amide derivatives, imide derivatives,tris{2-(methoxymethoxy)ethyl}amine, tris{2-(2-methoxyethoxy)ethyl}amine,tris[2-{(2-methoxyethoxy)methyl}ethyl]amine, and 1-aza-15-crown5.

[0129] The basic compound is preferably formulated in an amount of 0.001to 10 parts, and especially 0.01 to 1 part, per part of the photoacidgenerator. Less than 0.001 part of the basic compound fails to achievethe desired effects thereof, while the use of more than 10 parts wouldresult in too low a sensitivity and resolution.

[0130] Crosslinker

[0131] Formulated in the negative resist composition is an acidcrosslinker which forms a crosslinked structure under the action ofacid. Typical crosslinkers are compounds having at least twohydroxymethyl, alkoxymethyl, epoxy or vinyl ether groups within amolecule. Substituted glycoluril derivatives, urea derivatives, andhexa(methoxymethyl)melamine compounds are suitable as the acidcrosslinker in the chemically amplified, negative resist composition.Examples include N,N,N′,N′-tetramethoxymethylurea, hexamethylmelamine,tetraalkoxymethyl substituted glycoluril compounds such astetrahydroxymethyl substituted glycoluril andtetramethoxymethylglycoluril, and condensates of phenolic compounds suchas substituted or unsubstituted bis(hydroxymethylphenol) compounds andbisphenol A with epichlorohydrin. Especially preferred crosslinkers are1,3,5,7-tetraalkoxymethylglycolurils such as1,3,5,7-tetramethoxymethylglycoluril,1,3,5,7-tetrahydroxymethylglycoluril, 2,6-dihydroxymethylpcresol,2,6-dihydroxymethylphenol, 2,2′,6,6′-tetrahydroxymethylbisphenol A,1,4-bis[2-(2-hydroxypropyl)]benzene, N,N,N′,N′-tetramethoxymethylurea,and hexamethoxymethylmelamine. In the resist composition, an appropriateamount of the crosslinker is about 1 to 25 parts, and especially about 5to 20 parts by weight per 100 parts by weight of the solids in thecomposition. The crosslinkers may be used alone or in admixture of twoor more.

[0132] Other components

[0133] In the resist composition, a compound bearing a _C COOH group ina molecule may be blended. Exemplary, non limiting compounds bearing a≡CCOOH group include one or more compounds selected from Groups I and IIbelow. Including this compound improves the PED stability of the resistand ameliorates edge roughness on nitride film substrates.

[0134] Group I:

[0135] Compounds in which some or all of the hydrogen atoms on thephenolic hydroxyl groups of the compounds of general formulas (A1) to(A10) below have been replaced with —R⁴⁰¹—COOH (wherein R⁴⁰¹ is astraight or branched alkylene of 1 to 10 carbon atoms), and in which themolar ratio C/(C+D) of phenolic hydroxyl groups (C) to ≡CCOOH groups (D)in the molecule is from 0.1 to 1.0.

[0136] In these formulas, R⁴⁰⁸ is hydrogen or methyl; R⁴⁰² and R⁴⁰³ areeach hydrogen or a straight or branched alkyl or alkenyl of 1 to 8carbon atoms; R⁴⁰⁴ is hydrogen, a straight or branched alkyl or alkenylof 1 to 8 carbon atoms, or a -(R⁴⁰⁹)_(h)—COOR′ group (R′ being hydrogenor —R⁴⁰⁹—COOH); R⁴⁰⁵ is -(CH₂)_(i) - (wherein i is 2 to 10), an aryleneof 6 to 10 carbon atoms, carbonyl, sulfonyl, an oxygen atom, or a sulfuratom; R⁴⁰⁶ is an alkylene of 1 to 10 carbon atoms, an arylene of 6 to 10carbon atoms, carbonyl, sulfonyl, an oxygen atom, or a sulfur atom; R⁴⁰⁷is hydrogen, a straight or branched alkyl or alkenyl of 1 to 8 carbonatoms, or a hydroxylsubstituted phenyl or naphthyl; R⁴⁰⁹ is a straightor branched alkylene of 1 to 10 carbon atoms; R⁴¹⁰ is hydrogen, astraight or branched alkyl or alkenyl of 1 to 8 carbon atoms, or aR⁴¹¹COOH group; R⁴¹¹ is a straight or branched alkylene of 1 to 10carbon atoms; the letter j is an integer from 0 to 5; u and h are each 0or 1; s1, t1, s2, t2, s3, t3, s4, and t4 are each numbers which satisfys1+t1=8, s2+t2=5, s3+t3=4, and s4+t4=6, and are such that each phenylskeleton has at least one hydroxyl group; κ is a number such that thecompound of formula (A6) may have a weight average molecular weight of1,000 to 5,000; and λ is a number such that the compound of formula (A7)may have a weight average molecular weight of 1,000 to 10,000.

[0137] Group II:

[0138] Compounds of general formulas (A11) to (A1-5) below.

[0139] In these formulas, R⁴⁰², R⁴⁰³, and R⁴¹¹ are as defined above;R⁴¹² is hydrogen or hydroxyl; s5 and t5 are numbers which satisfy s5 ≧0,t5 ≧0, and s5+t5=5; and h′ is equal to 0 or 1.

[0140] Illustrative, nonlimiting examples of the compound bearing a≡CCOOH group include compounds of the general formulas AI-1 to AI-14 andAII-1 to AII-10 below.

[0141] In the above formulas, R″ is hydrogen or a CH₂COOH group suchthat the CH₂COOH group accounts for 10 to 100 mol % of R″ in eachcompound, a and K are as defined above.

[0142] The compound bearing a ≡C—COOH group within the molecule may beused singly or as combinations of two or more thereof.

[0143] The compound bearing a ≡C—COOH group within the molecule is addedin an amount ranging from 0 to 5 parts, preferably 0.1 to 5 parts, morepreferably 0.1 to 3 parts, further preferably 0.1 to 2 parts by weight,per 100 parts by weight of the base resin. More than 5 parts of thecompound can reduce the resolution of the resist composition.

[0144] The resist composition of the invention may additionally includean acetylene alcohol derivative for the purpose of suppressing formationof microbubbles in the resist solution. Preferred acetylene alcoholderivatives are those having the general formula (S1) or (S2) below.

[0145] In the formulas, R⁵⁰¹, R⁵⁰², R⁵⁰³, R⁵⁰⁴ and R⁵⁰⁵ are eachhydrogen or a straight, branched, or cyclic alkyl of 1 to 8 carbonatoms; and X and Y are each 0 or a positive number, satisfying 0≦X≦30,0≦Y≦30, and 0≦X+Y≦40.

[0146] Preferable examples of the acetylene alcohol derivative includeSurfynol 61, Surfynol 82, Surfynol 104, Surfynol 104E, Surfynol 104H,Surfynol 104A, Surfynol TG, Surfynol PC, Surfynol 440, Surfynol 465, andSurfynol 485 from Air Products and Chemicals Inc., and Surfynol E1004from Nisshin Chemical Industry K.K.

[0147] The acetylene alcohol derivative is preferably added in an amountof 0.01 to 2% by weight, and more preferably 0.02 to 1% by weight, per100% by weight of the resist composition. Less than 0.01% by weightwould be ineffective for improving coating characteristics andsuppressing micro bubbles, whereas more than 2% by weight would resultin a resist having a low resolution.

[0148] The resist composition of the invention may include, as anoptional ingredient, a surfactant which is commonly used for improvingthe coating characteristics. Optional ingredients may be added inconventional amounts so long as this does not compromise the objects ofthe invention.

[0149] Nonionic surfactants are preferred, examples of which includeperfluoroalkylpolyoxyethylene ethanols, fluorinated alkyl esters,perfluoroalkylamine oxides, perfluoroalkyl EO-addition products, andfluorinated organosiloxane compounds. Useful surfactants arecommercially available under the trade names Florade FC-430 and FC-431from Sumitomo 3M K.K., Surflon S-141 and S-145 from Asahi Glass K.K.,Unidine DS-401, DS-403 and DS-451 from Daikin Industry K.K., MegafaceF-8151 from DaiNippon Ink & Chemicals K.K., and X-70-092 and X-70-093from ShinEtsu Chemical Co., Ltd. Preferred surfactants are FloradeFC-430 from Sumitomo 3M K.K. and X-70-093 from ShinEtsu Chemical Co.,Ltd.

[0150] Pattern formation using the resist composition of the inventionmay be carried out by a known lithographic technique. For example, theresist composition is applied onto a substrate such as a silicon waferby spin coating or the like to form a resist film having a thickness of0.3 to 2.0 μm, which is then prebaked on a hot plate at 60 to 150° C.for 1 to 10 minutes, and preferably at 80 to 130° C. for 1 to 5 minutes.A patterning mask having the desired pattern is then placed over theresist film, and the film exposed through the mask to an ArF excimerlaser beam in a dose of about 1 to 100 mJ/cm², and preferably about 5 to50 mJ/cm², then postexposure baked (PEB) on a hot plate at 60 to 150° C.for 1 to 5 minutes, and preferably at 80 to 130° C. for 1 to 3 minutes.Finally, development is carried out using as the developer an aqueousalkali solution, such as a 0.1 to 5% (preferably 2 to 3%) aqueoussolution of tetramethylammonium hydroxide (TMAH), this being done by aconventional method such as dipping, puddling, or spraying for a periodof 0.1 to 3 minutes, and preferably 0.5 to 2 minutes. These steps resultin the formation of the desired pattern on the substrate. The desiredpattern may not be obtainable outside the upper and lower limits of theabove range.

[0151] The resist composition comprising the sulfonium salt of formula(1) is fully sensitive to ArF excimer laser light and has excellentsensitivity and resolution. It can form a relatively thick film which isadvantageous to etching. A finely defined pattern having sidewallsperpendicular to the substrate can easily be formed.

EXAMPLE

[0152] Examples of the invention are given below by way of illustrationand not by way of limitation.

[0153] The sulfonium salts (PAG1 to PAG8) of the following formulae wereexamined with respect to the sensitivity and resolution of resistcompositions formulated therewith.

Examples 1-41

[0154] Resolution of resist

[0155] Resist compositions were formulated by dissolving a sulfoniumsalt (PAG1 to PAG8) as the photoacid generator, a polymer (Polymers 1 to8) as the base resin, a dissolution regulator (DRR1 to DRR4), a basiccompound, and a compound having a ≡C—COOH group in the molecule (ACC1and ACC2) in a solvent containing 0.01% by weight of surfactant FC-430(Sumitomo 3M K.K.) in accordance with the formulation shown in Tables 1and 2. These compositions were each filtered through a 0.2μm Teflonfilter, thereby giving resist solutions.

[0156] The solvents and basic compounds used are as follows.

[0157] PGMEA: propylene glycol methyl ether acetate

[0158] CyHO: cyclohexanone

[0159] PG/EL: a mixture of 70% PGMEA and 30% ethyl lactate

[0160] TBA: tributylamine

[0161] TEA: triethanolamine

[0162] TMMEA: trismethoxymethoxyethylamine

[0163] TMEMEA: trismethoxyethoxymethoxyethylamine

[0164] These resist solutions were spin coated onto silicon wafers, thenbaked on a hot plate at 110° C. for 90 seconds to give resist filmshaving a thickness of 0.4 μm. The resist films were exposed using an ArFexcimer laser aligner (Lithotec Japan K.K.) and an ArF excimer laserstepper (Nikon Corporation; NA 0.55), then baked (PEB) at 110° C. for 90seconds, and developed with a solution of 2.38% tetramethylammoniumhydroxide in water, thereby giving resist patterns.

[0165] The resulting resist patterns were evaluated as described below.Provided that the dose which provides a 1:1 resolution at the top andbottom of a 0.25 μm line-and-space pattern is an optimum exposure (Eop,mJ/cm²), i.e., the sensitivity, the resolution of the resist underevaluation was defined as the minimum line width (μm) of the lines andspaces that separated at this dose. The shape of the resolved resistpattern was examined under a scanning electron microscope. It is notedthat sensitivity evaluation was made on all the resist compositionsusing the ArF excimer laser aligner, while resolution was evaluated onsome resist compositions using the ArF excimer laser stepper. Also, theresist solutions were held at 23° C. for 2 months before theirsensitivity was determined.

[0166] The formulation and test results of the respective resistcompositions are shown in Tables 1 and 2. TABLE 1 Photoacid DissolutionBasic Sensitivity Resolution Shape Sensitivity Example Resin generatorregulator compound Solvent (fresh) (fresh) (fresh) (aged)  1 Polymer 1PAG 1 TBA PGMEA 4.5 0.18 rectangular 4.3 (80) (1.5) (0.10) (480)  2Polymer 1 PAG 2 TBA PGMEA 5.2 — — 5.3 (80) (1.5) (0.10) (480)  3 Polymer1 PAG 3 TBA PGMEA 5.6 0.18 rectangular 5.8 (80) (1.5) (0.10) (480)  4Polymer 1 PAG 4 TBA PGMEA 4.8 — — 4.8 (80) (1.5) (0.10) (480)  5 Polymer1 PAG 5 TBA PGMEA 3.5 0.18 rectangular 3.6 (80) (2) (0.10) (480)  6Polymer 1 PAG 6 TBA PGMEA 5.0 — — 5.3 (80) (2) (0.10) (480)  7 Polymer 1PAG 7 TBA PGMEA 5.2 0.18 rectangular 5.5 (80) (2) (0.10) (480)  8Polymer 1 PAG 8 TBA PGMEA 5.5 — — 5.3 (80) (2) (0.10) (480)  9 Polymer 1PAG 1 TBA CyHO 4.6 0.18 rectangular 4.8 (80) (1.5) (0.10) (560) 10Polymer 2 PAG 1 TBA CyHO 4.8 — — 4.3 (80) (1.5) (0.10) (560) 11 Polymer3 PAG 1 TBA CyHO 4.3 0.18 rectangular 4.2 (80) (1.5) (0.10) (560) 12Polymer 4 PAG 1 TBA CyHO 4.8 — — 4.4 (80) (1.5) (0.10) (560) 13 Polymer5 PAG 1 TBA CyHO 5.2 0.18 rectangular 5.0 (80) (1.5) (0.10) (560) 14Polymer 6 PAG 1 TBA CyHO 5.5 — — 5.7 (80) (1.5) (0.10) (560) 15 Polymer7 PAG 1 TBA CyHO 4.6 0.18 rectangular 4.8 (80) (1.5) (0.10) (560) 16Polymer 8 PAG 1 TBA CyHO 4.8 — — 4.9 (80) (1.5) (0.10) (560) 17 Polymer9 PAG 1 TBA CyHO 5.5 — — 5.6 (80) (1.5) (0.10) (560) 18 Polymer 3 PAG 3TBA CyHO 5.5 — — 5.9 (80) (1.5) (0.10) (560) 19 Polymer 3 PAG 3 TEA CyHO5.8 — — 5.6 (80) (1.5) (0.10) (560) 20 Polymer 3 PAG 3 TMMEA CyHO 4.8 —— 5.0 (80) (1.5) (0.10) (560) 21 Polymer 3 PAG 3 THEMEA CyHO 4.0 — — 4.3(80) (1.5) (0.10) (560) 22 Polymer 6 PAG 4 TEA PG/EL 5.4 — — 5.2 (80)(1.5) (0.10) (480) 23 Polymer 6 PAG 4 DRR 1 TEA PG/EL 5.0 — — 5.2 (64)(1.5) (16) (0.10) (480) 24 Polymer 6 PAG 4 DRR 2 TEA PG/EL 4.8 — — 4.6(64) (1.5) (16) (0.10) (480) 25 Polymer 6 PAG 4 DRR 3 TEA PG/EL 4.6 — —4.6 (64) (1.5) (16) (0.10) (480)

[0167] TABLE 2 Photoacid Dissolution Basic Sensitivity Resolution ShapeSensitivity Example Resin generator regulator compound Solvent (fresh)(fresh) (fresh) (aged) 26 Polymer 6 PAG 4 DRR 4 TEA PG/EL 4.8 — — 4.8(64) (1.5) (16) (0.10) (480) 27 Polymer 7 PAG 3 TEA CyHO 4.9 — — 5.0(80) (1.5) (0.10) (560) 28 Polymer 7 PAG 3 DRR 1 TEA CyHO 4.4 — — 4.6(64) (1.5) (16) (0.10) (560) 29 Polymer 7 PAG 3 DRR 2 TEA CyHO 3.5 — —3.8 (64) (1.5) (16) (0.10) (560) 30 Polymer 7 PAG 3 DRR 3 TEA CyHO 3.9 —— 4.0 (64) (1.5) (16) (0.10) (560) 31 Polymer 7 PAG 3 DRR 4 TEA CyHO 3.8— — 4.0 (64) (1.5) (16) (0.10) (560) 32 Polymer 4 PAG 5 TEA CyHO 3.8 — —4.0 (80) (2) (0.10) (560) 33 Polymer 4 PAG 5 ACC 1 TEA CyHO 3.2 — — 3.0(80) (2) (2) (0.10) (560) 34 Polymer 4 PAG 5 ACC 2 TEA CyHO 3.0 — — 2.9(80) (2) (2) (0.10) (560) 35 Polymer 8 PAG 6 TEA PGMEA 5.3 — — 5.0 (80)(2) (0.10) (480) 36 Polymer 8 PAG 6 ACC 1 TEA PGMEA 5.0 — — 4.9 (80) (2)(2) (0.10) (480) 37 Polymer 8 PAG 6 ACC 2 TEA PGMEA 4.9 — — 5.0 (80) (2)(2) (0.10) (480) 38 Polymer 3 PAG 1 TEA PG/EL 4.8 — — 5.0 (40) (1.5)(0.10) (480) Polymer 5 (40) 39 Polymer 3 PAG 3 TEA PG/EL 4.9 — — 5.0(40) (1.5) (0.10) (480) Polymer 5 (40) 40 Polymer 5 PAG 1 TEA CyHO 4.8 —— 4.6 (40) (1.5) (0.10) (560) Polymer 7 (40) 41 Polymer 5 PAG 3 TEA CyHO3.2 — — 3.8 (40) (1.5) (0.10) (560) Polymer 7 (40)

[0168] For comparison purposes, the sulfonium salts (PAG9 to PAG19) ofthe following formulae were examined with respect to the sensitivity andresolution of resist compositions formulated therewith.

Comparative Examples 1-11

[0169] Using the sulfonium salts (PAG9 to PAG19), resist compositionswere similarly formulated. They were similarly evaluated for sensitivityand resolution.

[0170] The formulation and test results of the respective resistcompositions are shown in Table 3. TABLE 3 Compara- tive PhotoacidDissolution Basic Sensitivity Resolution Shape Sensitivity Example Resingenarator regulator compound Solvent (fresh) (fresh) (fresh) (aged) 1Polymer 1 PAG 9 TBA PGMEA 9.1 0.18 rectangular 9.3 (80) (1) (0.10) (480)2 Polymer 1 PAG 10 TBA PGMEA 9.9 — — 10.0 (80) (1) (0.10) (480) 3Polymer 1 PAG 11 TBA PGMEA 9.0 0.18 rectangular 9.5 (80) (1) (0.10)(480) 4 Polymer 1 PAG 12 TBA PGMEA 9.4 — — 9.6 (80) (1) (0.10) (480) 5Polymer 1 PAG 13 TBA PGMEA 8.9 0.20 some 9.0 (80) (1) (0.10) (480)positive taper 6 Polymer 1 PAG 14 TBA PGMEA 9.2 — — 8.8 (80) (1) (0.10)(480) 7 Polymer 1 PAG 15 TBA PGMEA 8.5 0.20 some 8.3 (80) (1) (0.10)(480) positive taper 8 Polymer 1 PAG 16 TBA PGMEA 9.2 — — 8.9 (80) (1)(0.10) (480) 9 Polymer 1 PAG 17 TBA PGMEA 5.5 — — 0.5 (80) (1) (0.10)(480) 10  Polymer 1 PAG 18 TBA PGMEA 4.8 — — 0.3 (80) (1) (0.10) (480)11  Polymer 1 PAG 19 TBA PGMEA 4.6 — — 0.1 (80) (1) (0.10) (480)

[0171] As seen from Tables 1 to 3, the resist compositions fallingwithin the scope of the invention have a higher sensitivity, resolutionand storage stability than the prior art compositions.

[0172] Japanese Patent Application No. 2000-077496 is incorporatedherein by reference.

[0173] Although some preferred embodiments have been described, manymodifications and variations may be made thereto in light of the aboveteachings. It is therefore to be understood that the invention may bepracticed otherwise than as specifically described without departingfrom the scope of the appended claims.

1. A resist composition comprising a base resin, a photoacid generator,and a solvent, wherein the photoacid generator is a sulfonium salt ofthe following general formula (1):

wherein R¹ is a monovalent cyclic or bridgedring hydrocarbon group of 3to 20 carbon atoms, R² is hydroxyl, nitro, halogen, or a straight,branched or cyclic monovalent hydrocarbon group of 1 to 15 carbon atomswhich may contain an oxygen, nitrogen, sulfur or halogen atom, K⁻ is anon nucleophilic counter ion, x is equal to 1 or 2, and y is an integerof 0 to
 3. 2. The resist composition of claim 1 wherein the base resinis a polymer having an alicyclic structure.
 3. The resist composition ofclaim 1 wherein the base resin is at least one polymer selected from thegroup consisting of polyacrylic acid and derivative thereof, a ternaryor quaternary copolymer of a norbornene derivative-maleic anhydridealternating polymer and polyacrylic acid or derivative thereof, aternary or quaternary copolymer of a tetracyclododecenederivative-maleic anhydride alternating polymer and polyacrylic acid orderivative thereof, a ternary or quaternary copolymer of a norbornenederivative-maleimide alternating polymer and polyacrylic acid orderivative thereof, a ternary or quaternary copolymer of atetracyclododecene derivative-maleimide alternating polymer andpolyacrylic acid or derivative thereof, polynorbornene, and metathesisringopened polymer.
 4. The resist composition of claim 1 wherein thebase resin is a polymer comprising recurring units of the followinggeneral formula (2) and having a weight average molecular weight of1,000 to 500,000,

wherein R⁰⁰¹ is hydrogen, methyl or CH₂Co₂R⁰⁰³; R⁰⁰² is hydrogen, methylor CO₂R⁰⁰³; R⁰⁰³ is a straight, branched or cyclic alkyl group of 1 to15 carbon atoms; R⁰⁰⁴ is hydrogen or a monovalent hydrocarbon group of 1to 15 carbon atoms having 10 a carboxyl or hydroxyl group; at least oneof R⁰⁰⁵ to R⁰⁰⁸ represents a monovalent hydrocarbon group of 1 to 15carbon atoms having a carboxyl or hydroxyl group while the remaining R'sindependently represent hydrogen or a straight, branched or cyclic alkylgroup of 1 to 15 carbon atoms, R⁰⁰⁵ to R⁰⁰⁸, taken together, may form aring, and in that event, at least one of R⁰⁰⁵ to R⁰⁰⁸ is a divalenthydrocarbon group of 1 to 15 carbon atoms having a carboxyl or hydroxylgroup while the remaining R's are independently single bonds orstraight, branched or cyclic alkylene groups of 1 to 15 carbon atoms;R⁰⁰⁹ is a monovalent hydrocarbon group of 3 to 15 carbon atomscontaining a —CO₂— partial structure; at least one of R⁰¹⁰ to R⁰¹³ is amonovalent hydrocarbon group of 2 to 15 carbon atoms containing a —CO₂—partial structure, while the remaining R's are independently hydrogen orstraight, branched or cyclic alkyl groups of 1 to 15 carbon atoms, R⁰¹⁰to R⁰¹³, taken together, may form a ring, and in that event, at leastone of R⁰¹⁰ to R⁰¹³ is a divalent hydrocarbon group of 1 to 15 carbonatoms containing a —CO₂— partial structure, while the remaining R's areindependently single bonds or straight, branched or cyclic alkylenegroups of 1 to 15 carbon atoms; R⁰¹⁴ is a polycyclic hydrocarbon grouphaving 7 to 15 carbon atoms or an alkyl group containing a polycyclichydrocarbon group; R⁰¹⁵ is an acid labile group; R⁰¹⁶ is a methylenegroup or oxygen atom; R⁰¹⁷ is a single bond or a straight, branched orcyclic alkylene group of 1 to 10 carbon atoms which may have a heteroatom-containing substituent; R⁰¹⁸ is hydrogen or an alkyl group of 1 to10 carbon atoms; k is equal to 0 or 1; a1, a2, a3, b1, b2, b3, c1, c2,c3, d1, d2, d3, and e are numbers from 0 to less than 1, satisfyinga1+a2+a3+b1+b2+b3+c1+c2+c3+d1+d2+d3+e =1.
 5. A chemically amplified,positive resist composition comprising a photoacid generator of thegeneral formula (1), a base resin according to claim 2 , 3 or 4 which issubstantially insoluble in a developer, but becomes soluble in thedeveloper under the action of an acid, and a solvent.
 6. The resistcomposition of claim 5 further comprising a basic compound.
 7. Achemically amplified, negative resist composition comprising a photoacidgenerator of the general formula (1), a crosslinker, a base resinaccording to claim 2 , 3 or 4 which is soluble in a developer, butbecomes insoluble in the developer after being crosslinked with thecrosslinker under the action of an acid, and a solvent.
 8. The resistcomposition of claim 7 further comprising a basic compound.
 9. A processfor forming a resist pattern comprising the steps of: applying a resistcomposition according to claim 1 onto a substrate to form a coating,heat treating the coating and then exposing it to radiation having awavelength of up to 200 nm through a photo mask, and optionally heattreating the exposed coating and developing it with a developer.